Design And First-Principles Calculations Of Molybdenum,Tungsten,Tantalum Sulfide And Halogen Doped Graphene Heterojunctions

Since the advent of graphene,opening its bandgap has been a research hotspot in the semiconductor field.Transition metal sulfides and graphene have similar structures and adjustable band gaps.This article intends to composite graphene with layered transition metal sulfides to form a heterojunction structure,to combine the energy band structure of two-dimensional transition metal sulfides and the excellent electron transport characteristics of graphene.A two-dimensional semiconductor material with adjustable bandgap and carrier concentration is designed.In recent years,due to the shortcomings of long experimental cycles and difficult synthesis,material design has been widely used in designing new materials and calculating related properties.In this paper,the first principles calculation system based on density functional theory is used to explore the influence of transition metal sulfide and transition metal sulfide/graphene heterostructure doped with halogen group elements（F,Cl,Br,and I）,including energy change and electronic properties;Structural stability and electronic properties of graphene/transition metal sulfide heterostructures;Structural stability and electronic properties of halogens doped graphene/transition metal sulfide heterostructures.This article constructs single-layer Mo S₂,WS₂,and Ta S₂ models,and conducts convergence testing and geometric optimization.Then,halogen group elements are doped on the surface of the optimized single-layer Mo S₂,WS₂,and Ta S₂ models by replacing atoms.The thermodynamic formation energy and electronic structure of the doped system are calculated.The results show that the defect formation energy of the heterojunction doped with F,Cl,Br,and I atoms gradually increase;Doping halide elements on the surface of single-layer transition metal sulfides can enhance their conductivity.Nine van der Waals heterojunction models were constructed by matching single-layer transition metal sulfides with graphene in different ways,and the variation of interface formation energy with the interlayer spacing of the heterojunction was calculated.The interface formation energy of all models showed a trend of first decreasing and then increasing with the increase of interlayer spacing,with the lowest energy value and the most stable structure near the interlayer spacing of 3.4～3.6?.The electronic structures of three relatively stable heterojunction models were calculated.It was found that graphene/Mo S₂ and graphene/WS₂had 1 me V and 2 me V band gaps,respectively,indicating that the band gap of graphene can be regulated by combining with transition metal sulfides to form a heterojunction.Finally,the four halogen elements F,Cl,Br,and I were doped into the S atom position of the transition metal sulfide layer in the three relatively stable heterojunctions.The results showed that the formation energy of F,Cl,Br,and I atoms doped with Mo S₂ and WS₂ on the heterojunction gradually decreased,and the work required for doping I atoms was the lowest.On the contrary,in Ta S₂ heterojunction,the formation energy of doped F,Cl,Br,and I atoms gradually increases.Among them,F atom doping is the easiest to achieve,while I atom doping is more difficult to achieve.In addition,the doping system introduces doping energy levels,which have a significant impact on the three heterojunction systems,resulting in a bandgap-free characteristic.Compared to the undoped heterojunction,the carrier concentration increases.